In the application of labels by what is known as transfer labeling, it is customary to position labels on a web and thereafter transfer the labels to the articles to be labeled. In one type of such labeling, heat-sensitive labels are used that must be heated and applied to the articles. In another type, pressure-sensitive labels are used that must be removed from the web and applied to the article. An improved apparatus that can be readily changed for use either for applying heat-sensitive labels or for applying pressure-sensitive labels is that disclosed and claimed in U.S. Pat. No. 5,250,129 issued in the name of Terence J. Twele and assigned to Owens-Illinois Plastic Products Inc., of Toledo, Ohio, assignee of record herein, which is incorporated herein by reference.
When applying such labels to articles of molded plastic composition, particularly blow-molded plastic containers composed of high density polyethylene or the like, in accordance with conventional technology it is necessary to delay application of the labels for a prolonged period of time, such as 24 hours, after removal of the containers from the mold in which they are fabricated to allow de-gassing of the container walls. Gases are trapped within the plastic material of the container walls as a result of the fabrication process, particularly in blow molding processes, and these gases must be allowed to migrate out of the container walls before running the containers through a labeling apparatus or process. Otherwise, if a pressure-sensitive or heat-sensitive label, particularly one made of non-breathable material such as a metalized pressure-sensitive label, is placed on the container prior to de-gassing, the residual gases that migrate out of the container wall material beneath the label will create bubbles beneath the label, thereby resulting in a defectively labeled product requiring costly re-processing and/or scrapage.
Of course, the prolonged delay period required for de-gassing after molding prior to transfer labeling of such plastic articles adds to production and hence product costs, particularly in a high volume mass production set-up. The de-gassing delay period entails mechanized transport equipment, storage space requirements, and added potential for damage to the article in such de-gassing processing intermediate the molding and labeling stations.
It is also common practice in the plastic container manufacturing art to imprint labeling information indicia on mold-fabricated plastic containers by employing a silk screening operation. Upon removal from the mold, the fabricated container is placed on a conveyor and conveyed successively through several stations, at one or more of which labeling information is silk screened onto one or more exterior surfaces of the container wall. Multiple stages are employed for multiple-color labeling and decorating.
Typical apparatus for printing or decorating by silk screening is shown in U.S. Pat. Nos. 4,005,649 and 4,398,627, and an improvement thereover is disclosed and claimed in U.S. Pat. No. 5,484,047 issued Jan. 16, 1996 in the name of John A. Plenzler and assigned to Owens-Illinois Plastic Products Inc., the aforementioned assignee of record herein, which is also incorporated herein by reference.
Such labeling of molded plastic articles by silk screen imprinting with typical silk screen ink materials, even when practiced on blow-molded plastic containers, does not require the aforementioned de-gassing delay period in the production process inasmuch as the labeling so applied to the container wall is inherently highly gas pervious or permeable since the ink-imprinted alphabetical and numerical characters are spaced from one another throughout the labeling and thus cover only a minor percentage of the exterior wall surface area available for out-gassing.